1. Field of the Invention
The present invention relates to a light-emitting element driving apparatus which drives light-emitting elements.
2. Description of the Related Art
Pulse width modulation (PWM) method is generally known as a preferable method for realizing a desired gradation by adjusting the amount of light emitted by a light-emitting element, such as, for example, a light-emitting diode (LED). Especially, when a light quantity correction for the LED is performed based on an adjustment of driving current value prior to gradation control of an LED, as changing the driving current value for the gradation control is difficult, the PWM method is preferably used for the gradation control.
However, according to the PWM method, the pulse width must be finely controlled, and the on/off control of a signal generates switching noise which is a significant source of problematic electromagnetic interference (EMI).
Furthermore, with the PWM method, problems will arise in a system which employs a combination of a plurality of LEDs of different luminescent colors to obtain a desired color. As the gradation is generally realized by changing the pulse width, that is, the gradation is realized by adjusting the ON time during which the current flows, substantial mixing of colors is realized only in a limited period of time, as shown in FIG. 8, and reproducibility of colors is not good.